(Not Applicable)
(Not Applicable)
This invention relates to antennas and, more particularly, to electronic scanning of a circular array antenna with excitation of a sum and difference beam pattern.
Electronic scanning of a circular array of radiating elements represents a long term problem area in antenna technology, particularly in the context of continuous circular scanning of a composite sum and difference beam pattern. The basic geometry of a circular array and the objective of providing the capability of uninterrupted and continuous scanning (e.g., from zero degrees to 360 degrees azimuth and continuing past 360 degrees) introduce complexities of signal switching and beam management and control. While solutions may have been proposed, no solutions free of operational limitations or of a high level of technical complexity are known.
Accordingly, objects of the present invention are to provide new and improved curved linear array antennas and such antennas having one or more of the following characteristics and capabilities:
circular arrays with continuously scannable beam patterns;
scannable sum and difference composite beam patterns;
stepped scanning of sum and difference beam patterns, with only two switch activations per step;
circular arrays with simplified switching networks;
stepped beam patterns formed by progressively modified element sub array;
circular scanning with a number of sub array elements not evenly divisible into the total array complement; and
circular scanning with sub arrays having an odd number of elements.
In accordance with the invention, an array antenna, with scannable beam sum and difference excitation, includes a circular array of radiating elements arranged to provide a beam pattern upon excitation of radiating elements of a sub array consisting of a fixed number of radiating elements of the array. First and second power dividers each have a first port and a plurality of divided power ports. A circuit device, coupled to the first ports of the first and second power dividers, is arranged to provide at a sum port a signal representative of a sum of signals from the power dividers and at a difference port a signal representative of a difference between signals from the power dividers. Switching devices are coupled between the radiating elements and the divided power ports of the first and second power dividers and arranged to provide the beam pattern by coupling the first and second power dividers to respective first left and first right subsets of a sub array of the radiating elements. A control facility is arranged to control the switching devices to scan the beam pattern by coupling the first power divider to a successive left subset of the radiating elements and the second power divider to a successive right subset of the radiating elements. Such successive left subset includes at least one radiating element not included in the first left subset and the successive right subset includes at least one radiating element not included in the first right subset. This switching protocol can then be repeated for continuing 360 degree scanning of the sum and difference pattern.
Also in accordance with the invention, an array antenna, with scannable beam excitation, includes a circular array of radiating elements arranged to provide a beam pattern upon excitation of a sub array consisting of a fixed number of radiating elements of the array and a power divider with a first port and a number of divided power ports equal to that fixed number. Switching devices are coupled between the radiating elements and the power divider and arranged to provide the beam pattern by coupling the power divider to the sub array of the radiating elements. A control facility is arranged to control the switching devices to scan the beam pattern by coupling the power divider to successive sub arrays, each modified from the preceding sub array by initiating coupling to a radiating element contiguous in a forward beam scan direction and terminating coupling to the trailing radiating element of the preceding sub array, to enable continuous 360 degree scanning.
For a better understanding of the invention, together with other and further objects, reference is made to the accompanying drawings and the scope of the invention will be pointed out in the accompanying claims.